Art of Measuring EC

Hydroponic gardening is easy and fun, if you know the basics! Hydroponic nutrient formulas provide all the essential elements needed for optimal plant growth, in a form that is immediately available to plants. But to maximize the benefits of hydroponics, it’s important to master the tools of the trade, especially EC and pH meters.

An EC meter is a great tool for measuring the strength of hydroponic nutrient formulas. EC stands for electrical conductivity. Pure water doesn’t conduct electricity, which means distilled water or RO-filtered water has an EC of about zero.

However, the more mineral ions (fertilizers) that are dissolved in the water, the more it conducts electricity. Measuring EC is a great way to determine if there is enough fertilizer in the water to meet the needs of plants. The higher the concentration of fertilizer salts dissolved in water, the higher the EC. The more diluted the nutrient solution, the lower the EC.

Feeding Plants for the Different Growth Stages

One of the most common mistakes beginners make is over-fertilizing. During the vegetative growth stage, plants prefer a milder nutrient formula—mostly water with just a small charge of nutrients. Low-to-medium EC promotes vegetative growth and makes it easier for young plants to take up water and nutrients.

Growers should start with a grow formula at half-strength during the vegetative stage. If you were to give young plants a full-strength dosage, it could choke them, restricting vegetative growth.

As the nutrient solution becomes saltier, it becomes harder for plants to take up water. If the EC becomes too high, especially under high temperatures, plants may not be able to take up enough water to meet basic needs.

The leaves could start to curl and turn brown around the edges, a condition known as fertilizer burn. If the nutrient solution becomes even saltier, it could pull water out of the roots, causing plants to wilt and die.

An EC meter takes all the guesswork out of properly fertilizing plants. Full-strength nutrient formulas usually have a target EC of about 1.8. During the vegetative growth stage, it’s best to keep the EC in the 1.2-1.6 range for most plants.

If the EC rises above 1.8 during the vegetative growth stage, just add more water to the reservoir to lower the EC. If the EC is too low, just add more fertilizer. It’s that simple!

Mature plants can handle full-strength nutrients as they enter the flowering stage. In fact, there is a direct, proportional relationship between EC and sugar content in the fruit. By gradually increasing the EC during the flowering stage, it becomes more difficult for plants to take up water.

In response, sugars condense in the fruit, and the plant produces more natural antioxidants as plant protection agents. Researchers at the University of Arizona doubled the lycopene content (red pigment) of tomatoes and raised vitamin C and other organic acids in fruits by more than 50% by raising the EC to highs of 5.

There is a trade-off, though. Fruits produced under high EC levels tend to be smaller and denser, and there may be an overall reduction in yields. Because of this, commercial growers rarely push EC to the limits, preferring to sacrifice overall quality to maximize yields.

Check Your Garden's EC Every Day

Whether you are a commercial grower or a hobbyist, it’s good to check the EC every day and adjust as necessary. For example, on a hot day with low humidity, plants will take up more water, leaving mineral salts behind and increasing EC levels. It will become necessary to top off the reservoir with fresh water.

On the other hand, during heavy fruiting and flowering, the plants may take up proportionally more minerals, leaving the water behind. In that case, the EC will tend to go down. During heavy flowering, you might want to top off with a little fertilizer after filling up the tank. Since many plants take up proportionally more potassium during heavy fruit and flower production, a potassium boost is a good way to put back in what the plant took out.

Replacing the Nutrient Solution

You should empty the reservoir and refresh the nutrient solution on a regular basis. Plants take up mineral ions at different rates in the various growth stages, so nutrient levels become unbalanced over time. The EC reading tells you the total dissolved solutes in the water, but it doesn’t tell you how much of each individual element remains in the nutrient formula.

Even if the EC is at the perfect target, the nutrient formula could be deficient in one or more elements. Some elements may build up in the reservoir over time, while other nutrients are drawn down. You should completely change the reservoir every 7-10 days for best results.

EC and Organic Fertilizers

EC is a great management tool for hydroponics, but it can be misleading when you’re using organic fertilizers because organic molecules generally don’t conduct electricity. Plants can’t take up large, uncharged organic molecules; they must first be digested by micro-organisms in the soil into tiny ions that plants absorb through the roots in a process called mineralization.

Micro-organisms such as mycorrhizal fungi and plant-growth-promoting rhizobacteria produce organic acids and enzymes that release the mineral ions from soil and organic matter into a form that the roots can absorb. In soil systems, organic fertilizers feed the micro-organisms, and the micro-organisms feed the plants. Only the ions that are ready for plant use will be measured with an EC meter.

Hydroponics provides a shortcut for mineral uptake. In hydroponics, the minerals are mined from the earth and processed into their water-soluble, ionic form. When hydroponic fertilizers dissolve in water, they immediately split up into a nutritious blend of positively and negatively charged mineral ions, bypassing the micro-organisms and directly feeding the plant.

By giving the plant all of its nutrients in water-soluble, ionic forms, the plant can take up nutrients quickly. Typically, plants will grow as much as 25% faster in hydroponics than in soil, and they will reach maturity sooner.

Environmental Conditions for Good EC

EC management also provides an accurate way of helping plants deal with changing environmental conditions. Under cool, low-light conditions, growers can raise EC levels to restrict vegetative growth and help reduce stretching. And during periods of high heat and low humidity, growers can lower the EC to ease plant stress.

Growers can also regulate the EC to make the crop more vegetative or more generative at the appropriate times, improving the colors, aromas and flavors of finished fruits and flowers.

EC vs. TDS

As a side note, there is some confusion about the relationship between readings from an EC meter and a TDS (total dissolved solutes) meter. The answer is pretty simple. TDS and EC meters both measure electrical conductivity. The only difference is an EC meter displays readings in millimhos (mmhos) and a TDS meter displays the readings in parts per million (ppm).

The TDS meter uses a conversion factor to display EC as an average ppm, usually at about a 700:1 ratio. In other words, an EC of 1 is approximately 700 ppm. Some manufacturers, however, use a 500:1 conversion factor. If you have a TDS meter and you’re not sure which conversion factor to use, it’s safest to use the 700:1 approximation.

Remember, it’s always better to err on the side of adding too little fertilizer than too much. If a plant starts to develop a nutrient deficiency, you can always give it a little of what it’s missing and it will come right back. If you over-fertilize, nutrients can build up to toxic levels in the plant.

To sum up, if you are new to hydroponics, keep it simple! Use half-strength nutrients during the vegetative growth stage, full-strength nutrients during the fruiting and flowering stage, and empty and replenish your nutrient reservoir on a regular basis.

You should get excellent results, even from your first crop! As you get to know your plants better, you will soon find ways to fine-tune your EC levels to maximize quality and yields.

By Harley Smith